The present invention relates to navigation and determining a location of a device, such as a communications device or the like, and more particularly to a method and device for trilateration using line of sight (LOS) link prediction and pre-measurement LOS path filtering to estimate or predict the location of a device or receiver.
Radio navigation techniques based on trilateration assume that the first signal to arrive at a receiver travels via the direct, Line of Sight (LOS) path from a transmitter or transmitting device to the receiver or receiving device. A navigation system may mistake a signal from a non Line of Sight (NLOS) path as the LOS signal if the LOS signal is attenuated by any attenuating objects in the LOS path such that it is not detectable at the receiver. Because the path length of a NLOS signal is greater than the LOS path length, the range estimate from a NLOS measurement will be in error by a positive amount. The cumulative effect from using multiple NLOS signals in a range estimate also results in a positive bias because all range measurements from NLOS signals are larger than the range measurements from LOS signals. Existing methods and devices initially assume that all LOS signals are detectable and measure ranges based on this assumption. Existing method and devices try to filter out NLOS signals after the measurement but such post-measurement filtering may result in an increased probability of error because NLOS ranging errors have already been introduced into the position estimate and because of a lack of information about performance of the paths and use of such information in the filtering process.